Automatic current limiting device for use in electrical signaling



Aug. 13, 1935. MATHlEu 2,010,875

AUTOMATIC CURRENT LIMITING DEVICE FOR USE IN ELECTRICAL SIGNALING Fil'ed May 11, 1929 4 Sheets-Sheet 1 4C ulk v aw 011.54 l'\//771 NZ. INVENTOR GASTON A. MATHEU v 7 ATTORNEY Aug. 13, 1935.

q. A. MATHIEU Filed- May 11; 1929 GASTEN ADEUN MATMEU ATTOR NEY Aug. 13, 1935. G. A. MATHIEU 2,010,875- AUTOMATIC CURRENT LIMITING DEVICE FOR USE IN ELECTRICAL SIGNALING Filed May 11, 1929 4 Sheets-Sheet 3 GASTON mwmusu ATTORNEY Aug. 13, 1935. s. A'. MA THIEU 2,010,875 AUTOMATIC CURRENT LIL IITING DEYICE FOR USE IN ELECTRICAL SIGNALING Filed May 11, 1929 4 Sheets-Sheet 4.

AA AAA Ylllxnnulnl INVENTOR r GASTON A. MATMEU ATTORN EY Patented Aug. 13, 1935 AUTOMATIC CURRENT LIMITING DEVICE FOR. USE IN ELECTRICAL SIGNALING Gaston Adelin Mathieu, London, England, as-

sign'orto Radio Corp poration of Delaware oration of America, a cor- Application May 11, 1929, serial No. 362,266 In Great Britain May 22, 1928 l 12 Claims. (01. 250-) This invention is for improvements in or modifications of the invention set forth in U.- S. application No. 239,843, filed Dec. 14, 1927, whichiresulted in U. S. Pat. #1,892,215, on Dec. 27, 1932,

:and relates a automatic limiting andregulating devices for use in electrical signaling. While not confined to its application thereto, the invention 7 anda plurality of relays energized by currents substantially proportional to the intensity of the signals to be limited and regulated and adapted to be actuated in succession by rising values of said intensity, so that the attenuation or weakening properties of the said intensity reducing means are varied according to variations in the said sig+ nal intensity.

In one arrangement briefly described in they above referred to application in which the. device was applied to a receiver comprising ahigh frequency'amplifier and a detector, the said device being insertedto regulate the current from the detector (or from a low frequency amplifier following the detector) itwas proposed to increase the range of regulation beyond that of the signal intensity reducing means by providing an additional relay adapted to be actuated if the signal strength rises above that necessary to actuate all the other control relays, and being arranged to switch'out one or more stagesof the. high frequency amplifier. V

i The arrangement was preferably such that the switching out of the stage or stages of the high frequency amplifier caused the direct current to drop to such a value that all but the first of the other relays were de-actuated, the re-installation of the said stage or stages of high frequency amplification being secured automatically by associating with the relayswitch winding co-operating with the first controlrelay an extra contact adapted to de-actuatethe relay controlling the i said stage or stages when the direct current strength had fallen sufliciently. In this way the range or control was nearly doubled.

The principal object of the present invention is to provide improved means for securing an increase of range of regulation, whereby said range may be increased to be more than twice the range of the signal intensity reducing means.

According to one modification of the present invention, in an installation comprising an auto-; matlc current limiting and regulating device, inserted to limit or regulate low frequency currents; there is provideclautomatic means for regulating the input to the automatic regulating device in-a "5 plurality of steps, said means being so controlled that for each step of input strength the auto? matic current limiting and regulating device gives its own rangc of regulation, the steps beingsuch that the whole effective range is substantially m continuous, i. e. broken only by the stepscf reg ulation efiected by the automatic current limiting; and regulating device.

In a furthermodification of my invention the means for regulating the input to the detector are 5 not actuated by relays in the automatic current limiting and regulating device but directly under the control of the output current from the said detector.

The invention is illustratcd in the accompanying diagrammatic drawings, in winch, Figure 1 shows an arrangement in whichthe intensity of, the signals impressed on the input elements of the amplifier stage is regulated, by means of relays actuated by current ,from the detector output; a

Figure 1A isa line diagram of the arrangement of Figure l;

Figure 2 shows an additional resistancenetwork to be used with-the modification shown in Figure l; V Figure 2A is a line diagram of the-arrangement of Figure l-including the additional amplitude control'means shown in Figure 2. L Figure 3 shows an arrangement in which the intensity of the signals impressed on the input elements of the amplifierare regulated directly. by the output current from the detector; I

Figure 3A is a line diagram. illustrative of the apparatus shown in Figures 3 and 4; while s Figure 4 showsa modification of Figure 3 in which high speed relays are interposed between the detector output and the control apparatus.

Referring to Figure l of the specification drawings TRI is an input transformer for a high frequency amplifier which is represented by two valves Vl, V2, in push-pull connection, the output from which works into a detector DE; shown' in Fig. 1A in whose output circuit is incorporated an automatic regulating device injaccordance with the disclosure of U. S. Pa-t.-No. 1,892,215. The secondaryof the transformer is associated with resistances Bl, R2 dimensioned in knownmanner to give proper terminal conditions to avoid reflection, and tapped as shown, the tappings being connected to fixed contacts Bea-5e and Gar-45c respectively. Each set of fixed contacts is associated with a wipe brush by or 69, the two brushes being keyed upon a common shaft S and being connected via contacts 5 and if to the grids of the valves VI and V2 respectively. In this waytheproportion of the signal strength in the transformer secondary, which is transferred direction (i. e. to increase the strength) by a similar magnet M2 operating through a pawl ia and ratchet wheel 4. The pawls 3a,, 2a are associated with springs Sp i, S122, adapted to bias them away from their respective ratchetwheels 3, t.

The terminal i and corresponding earthed point To are associated with an auxiliary contact (not shown) provided upon the last relay switch S5 of Figure 2 of U. S. Patent No. 1,892,215 incorporated in the automatic current limiting and regulating device in such manner'that when the said relay closes a circuit is completed from terminal I to earth Ia. The terminal 8 and corresponding earthed point 8a are associated with an auxiliary contact (not shown) provided upon the first relay switch SI of Figure 2 of the above referred to patent incorporated in the automatic current limiting and regulating device, the arrangement being such that the points 8, 8a. are connected together when the said relay opens. These connections between the current limiting relay RN and the control apparatus connected with RI and R2 are shown diagrammatically in Figure 1A.

3b, 4b are normally closed contacts adapted to be opened through the forks 30 40 respectively, when the associated pawls So. 'm are moved.

The function of the contacts 31 or 4b is to permit the spring SpI or $312 to return its associated pawl 30. or 4a to its initial position by opencircuiting one of the electro-magnets M2 or MI.

It will be seen that if the point 1 or B be connected to earth, by action of the switches S5 and SI, respectively, of Fig. 2 of U. S. Patent #l,892, 215, the action of the electromagnet M! or M2 and its associated spring Spi or S102, contact 31) or ib, and fork 30 or 40 will be to rotate the shaft S progressively in one direction or the other, until a contact lb or 21), bearing upon a slip ring He or 20 contacts with an insulated segment Id or 2:1 upon one of the slip rings when the circuit to the electromagnet Ml or M2 will be broken. The segments Id and 201 should be so positioned as to prevent the shaft S from being rotated in either direction beyond thedesigned limits of' movement for the brushes 5g, to.

In practice, the resistances R2 and RI, the wipe brushes 5g and Go, and their associated contacts, may be arranged within a screening box for the high frequency amplifier, all the other mechanism, including the electromagnets, being arranged outside this box.

1 Further, in order to reduce induction from the electro-magnet windings MI and M2, the said windings are preferably incorporated in a closed iron pot forming the armature of the electromagnet.

The tappings upon the resistances RI, R2 should be such that when the signal strength is rising, each step of the brushes 5g 6g in a direction to reduce the signal input into the detector will cause all the relays, except the first one, incorporated inthe automatic current limiting and regulating device, to open, while each step in a direction to increase the said input will cause all the said relays, except the last one, to close.

If these conditions be not fulfilled, it will be apparent that since the first and last relays of the automatic current limiting and regulating device control the magnets MI and M2, hunting or to and fro adjustment in the regulation of the high frequency input will result-an objectionable condition commonly met with in known regulating apparatus and giving rise to intermodulation, increase of noise level and distortion generally.

The operation of the apparatus shown in Figure l and the cooperation thereof with the amplitude control network and the actuating relays disclosed in detail and claimed in United States application #239,843, December 14, 1927, will be better understood by reference to the line diagram of Figure 1A in which A is the aerial; R indicates the receiver; RF indicates the high frequency amplifier which, in this instance, includes VI, V2 of Figure 1; DS is the detector; RN is the attenuation network and AF is the low frequency amplifier. The direct current component is taken from direct current amplifier DCA and used to energize the control relays CR which control attenuation network RN Up to this point the apparatus shown is substantially similar to the apparatus of Figure l of the United States application referred to above. In the present case, however, CR, that is the control relays, are connected in a manner and for a purpose set forth more in detail above in connection with the discussion of Figure l to the high frequency amplifier RF through the magnetic and mechanical relay MR. The object of the last connection is to control the resistances RI and R2 adapted to be inserted in the input circuit of the radio frequency amplifier in accordance with the positions of the first and final contact in the network resistance RN.

With the arrangement described, however, when the first relay in the automatic current limiting and regulating device operates, it causes operation of the magnet M2 which actuates the brushes 5g 6g to increasethe input into the high frequency amplifier to an amount such that all the relays, except the last, in the said automatic device operate, so that the same volume of low frequency output into the land-line or telephone receiver is maintained by a simultaneous increase in the high frequency input and a compensating decrease in the low frequency input into the low frequency amplifier.

l he fact that the change in the high frequency amplification issecured by the action'on one relay, while the compensation change on the low frequency side is obtained by the closing of a plurality, say, four relays, working in succession, necessarily involves two different transit times, which causes a momentary overload of the low frequency amplifier.

This sudden and momentary throw out of balance in the correct input of the respective high frequency and low frequency amplifiers, produces a kind of rushing noise in the telephone and, moreover, is apt ,to introduce a momentary paralysis of the low frequency amplifying valves.

Means should therefore be provided to avoid this defect. Such means may comprise an additional resistance network, introducing a. lossofi about 10 to 15 transmitting units into the input of the low frequency amplifier during the period due to the difference of time transit. Figure 2 of the specificationdrawings illustrates diagrammatically one arrangement of this kind. Referring to the said Figure 2, "OI, 02 represent the leads from the detector output, and LI, L2 the leads towards the output attenuating'network regulating the output power intothef low frequency land-lineor telephone amplifier; R P is a resistance network, similar to and adapted to be momentarily added to the resistance ntf work comprised in the automatic current limiting and regulating device. momentarily included in circuit by means 'of an auxiliary relay, comprising a winding WI and contacts I, 2, 3, 4, the winding WI being connected in parallel with the winding of the electromagnet M2. It will be seen that when the first relay in the automatic current limiting and regulating device moves to actuate the magnet -M2, the extra resistance R P will be momentarily inserted at the same time, as more input power is allowed into the high frequency amplifier. Byregulating the mechanical transit time of operation of the auxiliary relay (winding-WI) it is possible to obtain noiseless operation. Figure 2A is a line diagram showing the connection between the apparatus shown in Figure 2 of the present invention and the attenuation network and control relays and so forth shown in detail in the parent application. This line diagram is similar in many respects to the line diagram of Figure 1A differing therefrom in that the additional resistance network of Figure 2 is shown connected between the detector and the attenuation network and controlled by current which controls the resistances RI, R2 arranged to be inserted in the radiofrequency amplifier RF by theaction of the control relays CR. The purpose for the present arrangement is, as pointed out in detail above, to prevent overloading of the valves between the time when the change in resistance in RN is caused by the control relay and the time at which the change of resistance in the input circuit of the radiofrequency amplifier has been effected. j

The modification shown in Figure Set the accompanying drawings differs from the previously described arrangements mainly in that the means for regulating the input to the detector are not actuated by relays in the automatic current limiting and regulating device but directly under the control of theoutput current from the said detector. In Figure 3 of the accompanying drawings, parts which correspond to parts shown in Figure 1 of the drawings are indicated by like references.

Referring to Figure 3 of the accompanying drawings, it will be noted that the contacts 3?), 4b and fork mechanisms 30 4c are dispensed with, the points Ia, 2a being directly. connected to the points 8 and I respectively, and the cir-\ cuits for the solenoids MI M2 being completed through contacts 9c 8d and through contacts I I0 Iilc Id respectively. These contactsare asso ciated as shown, with relays B2 B3, in such manher that when relay B2 is energized, contact Id 1 is opened and contacts 80 9c closed, while when relay B3 is energized, contact 8d is opened and contacts IIlc IIc closed. The relays B2 B3 also actuate each a further pair of contacts 4c 50 or 6c 10, closing said contacts when the appropriate relay is energized. The output from the Theresist'a'nce R P is valves VI V2 is fed toa sensitive polarizedrelay BI which is biased toa desired degree by current flowing through an adjustable resistance RIE-in series with the relay winding. RSI, R62

are adjustable resistances whereby the sensitivity of the relay Bl may be adjusted. The tongue I20 of the relay BI co-operates with contacts I30 Me. As will be seen, when said relay is in its upper position, a battery E93 applies negative potential to the grid of a valve V3 through a circuit comprising armature I20, contact. I40, contacts '40 to, resistance R25 and battery Egl (assuming relay B2 to be in lie-energized position) while when relay Bi is in its lower position, potential is applied from the batteryEgS to the grid of the valve V4 through a circuit comprising armature Iic, contact I30, contacts to, To, resistance R4 and battery E92 (assuming relay B3 to be in de-energized position) The junction point of resistance REE? and battery EgI is connected to the cathode of the valve V3 through a resistance R3 and a condenser KI in parallel, and similarly a resistance-R5. and a condenser K2: are shunted across the grid circuit offlthe valve V3.

- anode current of said valve will rise sufficiently to energize relay B2, thus closing contacts 40 5c and breakingthe circuit of magnet M2. The condenser KI now begins to charge again, applying a gradually increasing-negative potential to the grid of valveV3, until the anode current of said valve falls to an extent sufficient to de-' energize relay B2, and opens contactdc So, at the same time closing the circuit of magnet M2. Thus magnetMZ will be energized ..nd deenergized successivelyduring the periods that arma ture I20 is against contact Me, the number of movements of the armature of the relay B2 per unitof time depending upon the value of the condenser KI, the resistance R3 and the other constants of the circuits. Similarly, while relay armature I20 is against contact I30, the magnet MI will be energized and de-energiz'ed successively. It will be noted that contacts 80 to of relay B2 are included in the circuit of magnet MI, whilecontacts I00 IIc of relay B3 are included in the circuit of magnet M2, and that the two magnets Ml M2 are therefore prevented from being energized together. The relay BI is adjusted so that armature I 20 contacts with one or other of its associated contacts when the a current in the detector valves VI V2 reaches a permissible maximum or a permissible minimum value.

Figure 4 of the accompanying drawings shows a slight modification of thearrangement shown in Figure 3, the modification consisting inproviding high speed relays B4 B5 arranged to be actuated by the relays B2 B3 instead of utilizing Figures 3 and 4. Will be more readily understood receiving by reference to Figure 3A, which is a line diagram of the apparatus of Figures 3 and 4 and of the apparatus described in detail in the parent application referred to above. This line diagram which is somewhat similar tov the line diagram of Figure 1A in some respects differs therefrom as for example the thermionic relay TB. is shown as being connected directly on the one hand to the detector separator output as shown more in detail in Figures 3 and l, and on the other hand to the input resistances of the detector'separato-r through MB. The resistances R5 and R2 are controlled partly in accordance with amplitude variations in the output of the detector separator and partly in accordance with the positions of the first and final movable contacts in the attenuation network which is shown as being connected to both the relay MR which is in turn connected to the input side of the detector separator.

It will be appreciated that the present invention, when applied to a radio receiver, secures a step by step regulation of the low frequency output by a combined regulation of the input allowed into both the high frequency and low frequency amplifierawithout changing the characcarrier and one side band is or are suppressed,

it is possible to employ apparatus in accordance with either the present or the parent invention, by transmitting for the purpose of effecting regulation an additional modulation frequency lying outside the frequency band of signal modulations, i. e. in the case of speech, by sending an additional modulation frequency lying outside the band, say, 500-2300 cycles. With such an arrangement it is merely necessary to filter out the additional frequency by means of a high or low pass filter from the output of the telephone detector (in the case of speech), rectify the said frequency and employ it for the control of the relays in the automatic current limiting and regulating device. Alternatively the additional frequency may lie within the. range of signaling frequencies, the same frequency in the signals being suppressed. For example, in the case of speech, the additional frequency may be one of 1500 cycles, a filter, preferably of the Wheatstone bridge type, being inserted in the output from the detector to prevent impulses of 1500 cycles frequency being passed on to the low frequency amplifier. It is found that such suppression of a single frequency does not materially affect the intelligibility of speech.

I claim:

1. In radio apparatus, thecombination of signal receiving means, amplifying means, detecting means associated with said amplifying means, low frequency .amplifying means, signal amplitude regulating means interposed between said receiving means and said amplifying means, a second signal amplitude regulating means interposed between said detecting means and low frequency amplifying'means, and means responsive to a current component obtained from said detecting means to control both of said amplitude regulating means.

2. In a radio receiver, high frequency signal means, high frequency amplifying means, detecting means connected to said amplifying means, low frequency amplifyingm'eans, amplitude regulating means interposed between said high frequency means and said detecting means, signal amplitude regulating means interposed between said detecting means and said low frequency amplifier, means associated with said detector for separating a uni-directional component therefrom, means actuated by said uni-directional component and responsive to amplitude variations therein for controlling both of said amplitude regulating, means, and a third amplitude regulating means actuated in accordance with variations in amplitude of said unidirectional current and operatively interposed I thereby between said detecting means and said low frequency amplifying means when the amplitude of the signals in said high frequency amplifier reachesa predetermined value.

.3. The method of receiving modulated high frequency energy which includes collecting modulated high frequency energy; amplifying the high frequency energy, rectifying the energy, amplifying the rectified alternating component of the rectified high frequency energy; and dissipating both the high frequency energy and its rectified alternating component in accordance with variations in amplitude of the uni-directional componentof the rectified high frequency energy.

45. In radio apparatus, the combination of means for receiving high frequency signals, detecting means, signal amplitude regulating means connecting said detecting means to said receiving means, amplifying means associated with the output circuit. of said detecting means, means operated in accordance with variations in amplitude of a uni-directional component obtained from said detecting means for controlling said amplitude regulating means, a resistance network, and means actuated by said uni-directional component for inserting said network between said detecting means and said amplifying means during the operation of said first named means.

5. An improvement in amplitude control means comprising an automatic current limiting and regulating device inserted in a translating system to limit low frequency currents therein and automatic means controlled by the intensity of the current fed to said limiting and regulating device for regulating the intensity of the current fed to said regulating device in a plurality of steps, said automatic means including switching devices and a pair of magnets adapted to drive said switching devices, means for generating electrical impulses and means controlled by the intensity of the current fed to said automatic currentlimiting and regulating device for feeding the generated impulses to said magnets.

6. An apparatus as claimed in claim 5 in which the means for generating electrical impulses comprisesa condenser and means for successively charging and discharging said condenser.

'7. An arrangement as claimed in claim 5 in which the means for generating electrical impulses comprises a condenser and the means for successively charging said condenser including a plurality of thermionic impulse generators, one associated with each magnet and a polarized relay energized in dependence upon the signal input to the automatic current limiting and regulating device.

8. A signaling system comprising, a device responsive to signal modulated carrier frequency energy, signal demodulating means connected means interposed between said demodulating means and said amplifier, and relays actuated by said selected direct current component for actuating said first and second named amplitude reg ulating devices.

9. The combination of a device for demodulating a signal modulated carrier wave and an amplifier connected with said demodulator, of a resistance network connected with the input of said demodulator to regulate the amplitude of the signal modulated carrier impressed thereon and a resistance network interposed between the output of said demodulator and the amplifier, of means for selecting a direct current component from the output of said demodulator, of thermionic means actuated by said direct current com- 'ponent to control the resistance network connected with the input of said demodulator, and automatic means for controlling the network between the demodulating device and said amplifier. I

10. An improvement in amplitude control apparatus comprising, an automatic current limiting and regulating device inserted in a line to limit or regulate low frequency currents flowing therein, and automatic means controlled by the intensity of the input to said automatic current limiting and regulating device for regulating said input in a plurality of steps, said automatic .means comprising, signal intensity reducing means, switchingmeans for controlling said signal intensity reducing means, and a pair of magnets or solenoids adapted to drive said switching means in one of two opposite directions, whereby said automatic current limiting and regulating device produces its own amount of regulation of input strength, the steps all being such that the whole effective range is continuous and broken only by the steps of regulation eifected by the automatic current limiting and regulating device.

11. A signaling system comprising, a thermionic demodulator tube having its input electrodes connected with a source of signal modulated carrier waves by way of an incoming line terminated by a tapped resistance, an output circuit connected with said demodulator tube, and means for controlling the amount of resistance interposed between said incoming line and said thermionic demodulator tube comprising, a second thermionic tube device energized by direct current components selected from the output circuit of said first name-d thermionic tube, a step-bystep device adapted when actuated to increase or decrease the amount of resistance interposed between said incoming line and said detector, and a magnetic relay associated with said stepby-step actuating device and energized by said second named thermionic tube.

Y 12. A signaling system comprising, a pair of thermionic demodulators having input and output electrodes, a circuit which'may be energized by signal waves tobe demodulated, said circuit including resistances, a plurality of contacts connected with points on said resistances, movable contact members connected with the input electrodes of said demodulators, said movable contacts and said contacts connected with points on said resistances being shaped so that a connection between said'circuit and said input electrodes is completed at all times, an output circuit connected with said demodulators, and means for controlling the amount of resistance interposed between said first namedicircuit and the input electrodes of said thermionic demodulators comprising, an additional thermionic tube device having its input electrodes energized when direct current components appearing in the output circuits of said first named thermionic demodulators rise above or fall below predetermined values, a step by step device adapted when actuated to move said movable contact members GASTON ADELIN MATHIEU. 

